/**
 * @file
 * ICMP - Internet Control Message Protocol
 *
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 *
 */

/* Some ICMP messages should be passed to the transport protocols. This
   is not implemented. */

#include "lwip/opt.h"

#if LWIP_ICMP /* don't build if not configured for use in lwipopts.h */

#include "lwip/icmp.h"
#include "lwip/inet.h"
#include "lwip/inet_chksum.h"
#include "lwip/ip.h"
#include "lwip/def.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"

#include <string.h>

/** Small optimization: set to 0 if incoming PBUF_POOL pbuf always can be
 * used to modify and send a response packet (and to 1 if this is not the case,
 * e.g. when link header is stripped of when receiving) */
#ifndef LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
	#define LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN 1
#endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */

/* The amount of data from the original packet to return in a dest-unreachable */
#define ICMP_DEST_UNREACH_DATASIZE 8

static void icmp_send_response(struct pbuf* p, u8_t type, u8_t code);

/**
 * Processes ICMP input packets, called from ip_input().
 *
 * Currently only processes icmp echo requests and sends
 * out the echo response.
 *
 * @param p the icmp echo request packet, p->payload pointing to the ip header
 * @param inp the netif on which this packet was received
 */
void
icmp_input(struct pbuf* p, struct netif* inp)
{
	u8_t type;
#ifdef LWIP_DEBUG
	u8_t code;
#endif /* LWIP_DEBUG */
	struct icmp_echo_hdr* iecho;
	struct ip_hdr* iphdr;
	struct ip_addr tmpaddr;
	s16_t hlen;

	ICMP_STATS_INC(icmp.recv);
	snmp_inc_icmpinmsgs();


	iphdr = p->payload;
	hlen = IPH_HL(iphdr) * 4;

	if(pbuf_header(p, -hlen) || (p->tot_len < sizeof(u16_t) * 2)) {
		LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short ICMP (%"U16_F" bytes) received\n", p->tot_len));
		goto lenerr;
	}

	type = *((u8_t*)p->payload);
#ifdef LWIP_DEBUG
	code = *(((u8_t*)p->payload) + 1);
#endif /* LWIP_DEBUG */

	switch(type) {
		case ICMP_ECHO:
#if !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING
		{
			int accepted = 1;
#if !LWIP_MULTICAST_PING

			/* multicast destination address? */
			if(ip_addr_ismulticast(&iphdr->dest)) {
				accepted = 0;
			}

#endif /* LWIP_MULTICAST_PING */
#if !LWIP_BROADCAST_PING

			/* broadcast destination address? */
			if(ip_addr_isbroadcast(&iphdr->dest, inp)) {
				accepted = 0;
			}

#endif /* LWIP_BROADCAST_PING */

			/* broadcast or multicast destination address not acceptd? */
			if(!accepted) {
				LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast or broadcast pings\n"));
				ICMP_STATS_INC(icmp.err);
				pbuf_free(p);
				return;
			}
		}

#endif /* !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING */
		LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));

		if(p->tot_len < sizeof(struct icmp_echo_hdr)) {
			LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));
			goto lenerr;
		}

		if(inet_chksum_pbuf(p) != 0) {
			LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo\n"));
			pbuf_free(p);
			ICMP_STATS_INC(icmp.chkerr);
			snmp_inc_icmpinerrors();
			return;
		}

#if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN

		if(pbuf_header(p, (PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
			/* p is not big enough to contain link headers
			 * allocate a new one and copy p into it
			 */
			struct pbuf* r;

			/* switch p->payload to ip header */
			if(pbuf_header(p, hlen)) {
				LWIP_ASSERT("icmp_input: moving p->payload to ip header failed\n", 0);
				goto memerr;
			}

			/* allocate new packet buffer with space for link headers */
			r = pbuf_alloc(PBUF_LINK, p->tot_len, PBUF_RAM);

			if(r == NULL) {
				LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: allocating new pbuf failed\n"));
				goto memerr;
			}

			LWIP_ASSERT("check that first pbuf can hold struct the ICMP header",
			            (r->len >= hlen + sizeof(struct icmp_echo_hdr)));

			/* copy the whole packet including ip header */
			if(pbuf_copy(r, p) != ERR_OK) {
				LWIP_ASSERT("icmp_input: copying to new pbuf failed\n", 0);
				goto memerr;
			}

			iphdr = r->payload;

			/* switch r->payload back to icmp header */
			if(pbuf_header(r, -hlen)) {
				LWIP_ASSERT("icmp_input: restoring original p->payload failed\n", 0);
				goto memerr;
			}

			/* free the original p */
			pbuf_free(p);
			/* we now have an identical copy of p that has room for link headers */
			p = r;
		} else {
			/* restore p->payload to point to icmp header */
			if(pbuf_header(p, -(s16_t)(PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
				LWIP_ASSERT("icmp_input: restoring original p->payload failed\n", 0);
				goto memerr;
			}
		}

#endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
			/* At this point, all checks are OK. */
			/* We generate an answer by switching the dest and src ip addresses,
			 * setting the icmp type to ECHO_RESPONSE and updating the checksum. */
		iecho = p->payload;
		tmpaddr.addr = iphdr->src.addr;
		iphdr->src.addr = iphdr->dest.addr;
		iphdr->dest.addr = tmpaddr.addr;
		ICMPH_TYPE_SET(iecho, ICMP_ER);

			/* adjust the checksum */
		if(iecho->chksum >= htons(0xffff - (ICMP_ECHO << 8))) {
			iecho->chksum += htons(ICMP_ECHO << 8) + 1;
		} else {
			iecho->chksum += htons(ICMP_ECHO << 8);
		}

			/* Set the correct TTL and recalculate the header checksum. */
		IPH_TTL_SET(iphdr, ICMP_TTL);
		IPH_CHKSUM_SET(iphdr, 0);
#if CHECKSUM_GEN_IP
		IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, IP_HLEN));
#endif /* CHECKSUM_GEN_IP */

		ICMP_STATS_INC(icmp.xmit);
			/* increase number of messages attempted to send */
		snmp_inc_icmpoutmsgs();
			/* increase number of echo replies attempted to send */
		snmp_inc_icmpoutechoreps();

		if(pbuf_header(p, hlen)) {
			LWIP_ASSERT("Can't move over header in packet", 0);
		} else {
			err_t ret;
			ret = ip_output_if(p, &(iphdr->src), IP_HDRINCL,
			                   ICMP_TTL, 0, IP_PROTO_ICMP, inp);

			if(ret != ERR_OK) {
				LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ip_output_if returned an error: %c.\n", ret));
			}
		}

		break;

		default:
			LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ICMP type %"S16_F" code %"S16_F" not supported.\n",
			                         (s16_t)type, (s16_t)code));
			ICMP_STATS_INC(icmp.proterr);
			ICMP_STATS_INC(icmp.drop);
	}

	pbuf_free(p);
	return;
lenerr:
	pbuf_free(p);
	ICMP_STATS_INC(icmp.lenerr);
	snmp_inc_icmpinerrors();
	return;
#if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
memerr:
	pbuf_free(p);
	ICMP_STATS_INC(icmp.err);
	snmp_inc_icmpinerrors();
	return;
#endif /* LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN */
}

/**
 * Send an icmp 'destination unreachable' packet, called from ip_input() if
 * the transport layer protocol is unknown and from udp_input() if the local
 * port is not bound.
 *
 * @param p the input packet for which the 'unreachable' should be sent,
 *          p->payload pointing to the IP header
 * @param t type of the 'unreachable' packet
 */
void
icmp_dest_unreach(struct pbuf* p, enum icmp_dur_type t)
{
	icmp_send_response(p, ICMP_DUR, t);
}

#if IP_FORWARD || IP_REASSEMBLY
/**
 * Send a 'time exceeded' packet, called from ip_forward() if TTL is 0.
 *
 * @param p the input packet for which the 'time exceeded' should be sent,
 *          p->payload pointing to the IP header
 * @param t type of the 'time exceeded' packet
 */
void
icmp_time_exceeded(struct pbuf* p, enum icmp_te_type t)
{
	icmp_send_response(p, ICMP_TE, t);
}

#endif /* IP_FORWARD || IP_REASSEMBLY */

/**
 * Send an icmp packet in response to an incoming packet.
 *
 * @param p the input packet for which the 'unreachable' should be sent,
 *          p->payload pointing to the IP header
 * @param type Type of the ICMP header
 * @param code Code of the ICMP header
 */
static void
icmp_send_response(struct pbuf* p, u8_t type, u8_t code)
{
	struct pbuf* q;
	struct ip_hdr* iphdr;
	/* we can use the echo header here */
	struct icmp_echo_hdr* icmphdr;

	/* ICMP header + IP header + 8 bytes of data */
	q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
	               PBUF_RAM);

	if(q == NULL) {
		LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
		return;
	}

	LWIP_ASSERT("check that first pbuf can hold icmp message",
	            (q->len >= (sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));

	iphdr = p->payload;
	LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
	ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
	LWIP_DEBUGF(ICMP_DEBUG, (" to "));
	ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
	LWIP_DEBUGF(ICMP_DEBUG, ("\n"));

	icmphdr = q->payload;
	icmphdr->type = type;
	icmphdr->code = code;
	icmphdr->id = 0;
	icmphdr->seqno = 0;

	/* copy fields from original packet */
	SMEMCPY((u8_t*)q->payload + sizeof(struct icmp_echo_hdr), (u8_t*)p->payload,
	        IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);

	/* calculate checksum */
	icmphdr->chksum = 0;
	icmphdr->chksum = inet_chksum(icmphdr, q->len);
	ICMP_STATS_INC(icmp.xmit);
	/* increase number of messages attempted to send */
	snmp_inc_icmpoutmsgs();
	/* increase number of destination unreachable messages attempted to send */
	snmp_inc_icmpouttimeexcds();
	ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
	pbuf_free(q);
}

#endif /* LWIP_ICMP */
